The development of a powergrid in the intermountain west would bring electricity to millions of homes, potentially from renewable energy sources such as wind, solar, and geothermal. The new grid’s transmission lines may also create more habitat for the Common Raven, a pervasive predator on less common prey.

Construction of the 1000-mile Gateway West, one of seven priority transmission projects, will traverse a large tract of sagebrush steppe in Idaho and Wyoming. Sagebrush is home to several species of conservation concern, including the Greater sage-grouse, a drab chicken-sized game bird with a highly specialized mating display. Ravens prey on sage-grouse chicks and eggs, and they may be more likely to search for them near their own nests. Ravens preferentially nest on elevated structures, such as trees or cliffs, which are generally limited in open sagebrush habitat. Hypothetically, transmission lines built through sage-grouse breeding areas could increase raven nest site availability and abundance, resulting in a decrease in sage-grouse or other wildlife populations.

A three-year study at the U.S. Department of Energy Idaho National Laboratory investigated raven reliance on transmission lines for nesting. The existing lines in the study area turned out to be an important resource for the opportunistic birds. Seventy-two percent of raven nests observed were built on transmission lines or other artificial structures, and nest sites were closer to the lines than a random sample of unused sites. The results strongly suggest that transmission lines facilitate sagebrush proliferation by the avian predators.

The influence of raven abundance or transmission lines on sage-grouse populations is more difficult to quantify. Preliminary research by biologists in Nevada showed sage-grouse nests located farther from power lines had higher survival rates. Ravens may factor into the lower nest success, and conceivably, more ravens on the power line trail would eat more sage-grouse chicks and eggs.

The implications of the Idaho study extend to other species. The proposed southwest transmission sections, TransWest Express and SunZia, could bring more ravens into contact with already declining populations of desert tortoise and loggerhead shrike. Thoughtful siting and other planning measures will hopefully mitigate the impact of energy development on wildlife. We shouldn’t have to choose between clean energy and a clear conscience.– Miles Becker| 20 January 2014

Source: Howe, K.B. et al. 2014. Selection of anthropogenic features and vegetation characteristics by nesting Common Ravens in the sagebrush ecosystem. The Condor: Ornithological Applications

2 Comments

The article states that nests located farther from powerlines had higher survival rates. However that it not what the study found! To accurately reflect the Nevada study, the article should have said that sage grouse nest survival was not found to be influenced by distance from the transmission line. Below is a quote from the article which states the opposite. “In the nest survival analyses, distance from Falcon-Gondor was not supported in model results, and its parameter estimate was not significant. In the pre-fledging chick survival analyses, distance from the Falcon-Gondor transmission line was supported in model results and the parameter estimate was significant. However, the negative influence of distance from the Falcon-Gondor transmission line suggests that early chick survival was higher if the brood was located closer to the transmission line, which may potentially be confounded with differences in pre-fledging chick survival between the Roberts and Cortez populations. In the female survival analyses, we did not find support for an influence of nest distance from the Falcon-Gondor transmission line on spring, fall, or annual survival. In the male survival analyses, model results supported an interaction between the amount of wildfire footprint surrounding a lek and the distance of the lek from the Falcon-Gondor transmission line on survival of males. However, this interaction suggests that annual survival for males is higher for males that attend leks closer to the transmission line.”

As a science magazine, you need to make sure the results are reported accurately.

The quote provided in the comment above is from a February 2013 Progress Report on a study in west-central Nevada. The Conservation article refers to the most recent report from the same research lab, which is expected to be released in 2014. Those data strongly suggest female sage-grouse and nest survival is related to distance from powerlines, as reported accurately here. The authors requested their preliminary data be withheld from public viewing until later in the peer-review process. Quotable text will make its way onto the research lab’s linked website or into the pages of a journal in the near future.